M67/NGC 2682 - LRGB

BTW, is that a full frame image or have you scaled/cropped the image from the original size?

My master image is 1600x1200 pixels (the size of my ST-2000XM imaging chip). The large image you see is 75% of the original (ie. scaled to 3/4 of the original). The smaller image you see when you first visit the associated web page is also a resampling of the original (41% so as to get a 650 pixel width and thereby fit nicely on my monitor along with the details to the left and right of the image).

Just wondering, when it comes to background noise etc, do you ever use the "Replace Colour" function or have you a better way around it?

Nice one Tony,

I will have to start imging clusters before you copyright all of them. I tried the Beehive one night with poor skies but I got no colour difference in the stars at all. I guess its much more difficult than it seems since the colour variation will be very subtle.

Kieran

Just wondering, when it comes to background noise etc, do you ever use the "Replace Colour" function or have you a better way around it?

Hi Michael,

I never use something like "replace colour" since I would be altering the original data. My management of the black point effectively determines how my background will appear.

To be more specific, I will normalize my three RGB channels and then proceed with the midtones and then the black and white points.

Since such images (stars) have a high S/N ratio (especially with my 3- and 6-min subs), background noise is never an issue. My second to last step during processing is the "despeckle" command within the Filters->Noise menu but that is it (and its impact is nominal at best).

Nice one Tony,

I will have to start imging clusters before you copyright all of them. I tried the Beehive one night with poor skies but I got no colour difference in the stars at all. I guess its much more difficult than it seems since the colour variation will be very subtle.

Hi Kieran,

If you have trouble getting colouration with your stars and everything seems white, I suspect the problem is that your burning out the cores. There is a delicate balance between the luminance and the RGB layering. We need sufficient RGB data (exposure) to capture the colours and sufficient luminance data so as not to overwhelm the RGB data.

My starting point is always the histogram when imaging LRGB since it will show me the kind of signal I have and which always forms the basis of my starting point.

I never use something like "replace colour" since I would be altering the original data. My management of the black point effectively determines how my background will appear.

The idea of the "replace colour" function in what I was thinking isn't that you would replace the colour per se, as the name would suggest. Rather it's how it allows you to select data. The function can be used to select the noisiest data, the data in the darkest parts of the image. Then, you could just simply reduce the brightness of this data. Much the same as adjusting levels or curves I guess.